Radio ham installing a 20ft high ariel mast?

near neighbour into radio receiving and broadcasting on a worldwide basis, and looks like hes going to erect a triangular radio mast about 20ft in length plus probably another 20 ft for the ariel in his garden,anyone know what the laws are concerning radio hams installing these masts?and would his broadcasting interfere with my radio and television signals,Im asking this question as i live in a poor reception area for radio/ tv signals.any info greatly appreciated